A large number of observations suggest that microtubules are involved in cell shape changes during various developmental processes and in the translocation of particles and organelles in processes such as anaphase chromosome movement, axoplasmic transport and the movements of lysosomes. The broad objectives of this research project are to provide an understanding of how microtubules might produce and control the force necessary for these processes. Flagellar outer doublet microtubules will be used as a model system to examine the mechanism of mechanochemical coupling to microtubule sliding. Specifically, the goal of this research is to determine the pathway of adenosine triphosphate hydrolysis by dynein and to examine the mechanism by which hydrolysis is coupled to dynein crossbridge motion to produce active sliding of outer doublet microtubules. The pathway will be determined through the use of rapid transient kinetics and isotope exchange methods to measure ATP binding, hydrolysis and product release. Steps in the adenosine triphosphate hydrolysis pathway will be correlated with steps in the crossbridge cycle by measuring the kinetics of association and dissociation of the dynein-tubulin complex. These studies should provide a better basis to examine the production and control of force in other microtubule systems.